Saturday, November 3, 2012

Great woods burn

The weather finally cooperated, a good crew was available, and on Thursday, Nov. 1, 2012, we were able to accomplish the planned burn on our north-facing woods. 26 acres of mixed oak woods. Kathie's estimate on the day after the burn was over 90% burn coverage, which is the best we have ever been able to do. Next to a skilled crew, the most important thing for a successful burn is the right weather, and we had it.

We have a biennial schedule for the north-facing oak woods and this was the year to burn. Because of the drought, all the leaves of the big oaks were down; there was plenty of fuel. The major rainfall in late October, however, complicated matters, but finally at the end of October the weather cleared. Between the sun and wind, the fuel (oak leaves) dried off, although heavy dew slowed things down and on the day of the burn we waited until noon to get started.

We had a skilled crew. In addition to our own crew (Susan and Amanda) and an experienced volunteer (Michael) we had personnel from both Integrated Restoration and Michler/Brown.

We had constructed a fire break around the whole periphery, starting at the hilltop with the North Fire Break. A mowed/blown break went from there down the hill to County F at both ends.

Lighting along the edge of the North Fire Break

Lighting (with two crews) began in the middle at the top (see "Start of lighting" on the map). One crew went east, the other west, following the fire break at the top of the hill. Because of the wind, this was a backing fire across the top of the hill. Several "waters" spread out following each drip torch, keeping an eye out for spot fires. It took each crew about an hour to reach their end of the North Fire Break, and another hour to reach the bottom of the hill at County F.

The fire spreading out from the North Fire Break.

Once the whole woods was ringed, interior lighting (stripping) could be started. The northwest wind and the steep hill resulted in a head fire, but because the principal fuel was oak leaves, flame heights were not high.

We also lighted the County F road cut, which has a lot of great savanna herbs (see Michael's photo below).

The County F road cut burned very well (photo by Michael)

By 3:30 PM the whole woods was burning and attention was then turned to mop-up at the sides and top of the hill. A few tall snags near the top of the hill presented problems, and chain saws had to be brought in. (You don't start an oak woodland burn without a couple of chain saws ready.) Everything had been wrapped up by 5 PM.

Next day Kathie and I came back to survey the results. By this time all the smokers had gone out. There is a middle footpath that extends the whole length of the north woods and Kathie used that for access. From that mid point she could look both up and down and assess the extent of burn coverage, which was at least 90%, perhaps more.

White oaks rising out of ashes at the east end of the burn unit.

Close up of the burn. Most of the fuel was oak leaves.

A very successful burn, the best we have ever had on the north woods.

A question that often comes up: which is better, a spring or fall burn? For prairies and savannas, either works, but for north-facing oak woodlands, fall burns are preferable. There are several reasons:

The principal fuel, oak leaves, is newly fallen and very flammable. In the spring, especially in a big snow year, the leaves are flattened, soaked with water, and thus burn poorer.

Snow is not a problem in the fall. In the spring, especially in a large snow year, the snow may remain even into April, thus preventing a burn. Once the snow does melt, it may take quite a while for the oak leaves to dry out enough to burn well.

In fall all the native vegetation has senesced and will not be affected by the burn. In the spring, many early species will have already developed and will be knocked back by the burn. With poor timing, a year of development may be lost.

However, the fall burn season is generally very short, and if you aren't paying attention you could miss it completely.

For north-facing oak woods, it is thus best to try for a fall burn. If you miss it, you still have the spring ahead of you.

Burning a wide black line at the top of the hill. This is important to protect the oak savanna areas.